1. Field of the Invention
This invention concerns a power converter device that transforms a direct current input voltage into several outputs. This multi-output converter provides a regulated main output and also regulates one of a plurality of auxiliary outputs and is of special application in equipment that requires more than one regulated direct-current power supply voltage.
2. Description of the Prior Art
The article by J. Sebastian, J. Blanco, J. Uceda, A. Lumbreras and F. Canizales, "AN ALTERNATIVE METHOD FOR CONTROLLING TWO-OUTPUT DC-TO-DC CONVERTERS USING SATURABLE CORE INDUCTORS", PESC 1990, shows the regulation of two outputs of a converter using a single switching element and a saturable core inductor, as illustrated in FIG. 11b of the article mentioned.
The regulation of the two converter outputs is achieved by modulation of the switching frequency and of a pulse width of a duty cycle of a MOSFET.
The main output is regulated by means of the pulse width of the duty cycle of the MOSFET and the auxiliary output is regulated by the switching frequency of the MOSFET in question. Nevertheless, when oscillations occur in the auxiliary output load, it is accompanied by a variation in the switching frequency.
The switching frequency varies by a percentage of the oscillation in the load connected to the auxilliary output. The drawbacks resulting from variations in switching frequency reside in the greater size required of the magnetic components, such as a transformer and inductors, for the lowest switching frequency. Other parts of the converter that are also penalized in the design process are electromagnetic interference filters since the switching frequency moves over a broad range, meaning that the design of these filters is of greater complexity.
Similarly the efficiency of the converter is also affected as switching losses in the MOSFET and in the magnetic circuit of the transformer are proportional to the switching frequency, making the losses increase and the efficiency fall.